As a woman’s body mass index rises before she is pregnant or early in pregnancy, there is an increased risk of fetal death, stillbirth or infant death, and severely obese women have the highest risk, researchers said Tuesday.

Mary Macvean, Los Angeles Times, Apr 15, 2014

But even “modest” increases in BMI were associated with increased risks, the scientists wrote in the Journal of the American Medical Assn.

The scientists recommend that women and their caregivers take the findings into account as they consider getting pregnant. They note that the optimal BMI - calculated as weight in kilograms divided by height in meters squared - for pregnancy has not been established for preventing fetal and infant death.

Worldwide, about 2.65 million stillbirths occurred in 2008; an estimated 3.6 million infants die each year before the age of 28 days.

The researchers looked at 38 studies from various parts of the world, 25 of them from Europe and North America, to analyze BMI and fetal and infant death, and concluded “moderate to strong increases in the relative risk of fetal death, stillbirth, neonatal death, perinatal death and infant death were found with increasing maternal BMI.”

Women with a BMI of 40, or severely obese, had about a two- to three-fold increase in risk, compared with women whose BMI measured 20, wrote the researchers, who were from Imperial College London, Oslo University, Loma Linda University and other institutions.

They suggested several possible mechanisms, including that being overweight has been associated with a risk of gestational diabetes and hypertension and other conditions that put the fetus and child at risk.